return api.get(mapUrl).then(function (response) {
          var map = sourceMap.SourceMapConsumer(response.body);
          var position = positionOf(js, 'return"browserify-server-test"');
          expect(position).to.exist;

          expect(map.originalPositionFor(position)).to.eql({
            source: 'browserify-server-test',
            line: 2,
            column: 0,
            name: null
          });
        });
function applySourceMap(
  generatedId: string,
  url: string,
  code: string,
  mappings: Object
) {
  const generator = new SourceMapGenerator({ file: url });
  mappings.forEach(mapping => generator.addMapping(mapping));
  generator.setSourceContent(url, code);

  const map = SourceMapConsumer(generator.toJSON());
  setSourceMap(generatedId, Promise.resolve(map));
}